In conventional exercise machines, an exercise bar is pulled or pushed from a fixed start position. For example, some machines have a bar presented in position before a standing, seated, or kneeling user who pulls the bar downward, pushes it in a direction away from the user, or pivots it laterally against a selected weight resistance. Such machines can be used for multiple types of exercises by the user assuming different positions relative to the position of the bar and to its predefined range of travel. However, these systems have the problem that the position of the bar is not adjustable to accomodate the particular size of an individual user or the type of exercise to be performed.
Moreover, conventional exercise systems are primarily directed to users standing, seated or kneeling in an upright position. For some types of exercise, such as bent leg pulling or pushing, it is highly desirable to have a machine which accomodates the user in a lying or horizontal position. Some machines employ horizontal platforms positioned under a bar which can be pulled or pushed while the user is lying down. For example, in U.S. Pat. No. 4,200,279, a horizontal platform has a pivot bar arranged at one end which is connected by cam and pulley to a stack of weights for doing knee pushing, hamstring pulling, or sit-ups. However, this machine has the pivot bar in a fixed position relative to the horizontal platform, which limits the types of horizontal exercises which can be comfortably performed and does not readily accomodate the physical dimensions of different users. Also, the pivot bar has only a fixed start position of travel which cannot be adjusted.
Another horizontal exercise machine shown in U.S. Pat. No. 4,226,415 has a horizontal platform and a pivot bar which can be adjusted in its horizontal position or vertical height above the platform. A two-way rotary hydraulic actuator is used to provide a constant resistance to the pivot motion of the bar in one or the other direction. Although the resistance bar can be adjusted in position for different types of exercises and for different dimensions of users, it has the drawback that the start position of the bar's travel cannot be preset by a user for exact repetition of a selected exercise. Instead, the bar is moved against resistance to an arbitrary end of stroke by the user and then returned to an arbitrary start of the next stroke. The inability to exactly repeat an exercise stroke has the disadvantage that the user cannot reliably gauge progress to be made by repetition of the same strokes.